Power surge landing system

ABSTRACT

An aircraft landing system is disclosed. In various embodiments, an aircraft landing system as disclosed herein includes a processor that determines to start a final stage of descent for the aircraft. The processor determines a set of commands for actuators of the aircraft, based on the determination to start the final stage of descent, to flare the aircraft while wings of the aircraft are substantially in a forward flight position followed by transitioning to a vertical tilt position and completing the landing in substantially vertical flight. The commands are provided to the actuators of the aircraft.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 15/447,029, entitled POWER SURGE LANDING SYSTEM filed Mar. 1,2017 which is incorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Landing an aircraft may require large amounts of power over a longperiod of time. Landing an aircraft may cause the aircraft's engine tooverheat. Traditional methods of landing may be susceptible to humanerror or safety issues.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a diagram illustrating an embodiment of an aircraft's batterydischarge curve.

FIG. 2 is a diagram illustrating an embodiment of power used by anaircraft utilizing a power surge landing system.

FIG. 3 is a diagram illustrating an embodiment of an aircraft comprisinga power surge landing system.

FIG. 4 is a diagram illustrating an embodiment of a power surge landingsystem.

FIG. 5A is a diagram illustrating an embodiment of an aircraftcomprising a power surge landing system.

FIG. 5B is a diagram illustrating an embodiment of an aircraftcomprising a power surge landing system.

FIG. 6A is a diagram illustrating an embodiment of a tiltwing aircraftin a neutral wing position.

FIG. 6B is a diagram illustrating an embodiment of a tiltwing aircraftin a tilted wing position.

FIG. 7A is a diagram illustrating an embodiment of a landing processenacted by a power surge landing system in a tiltwing aircraft.

FIG. 7B is a diagram illustrating an embodiment of wing positioningenacted by a power surge landing system.

FIG. 8 is a flow diagram illustrating an embodiment of a power surgelanding system process.

FIG. 9 is a flow diagram illustrating an embodiment of a power surgelanding system process.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; a composition of matter; a computerprogram product embodied on a computer readable storage medium; and/or aprocessor, such as a processor configured to execute instructions storedon and/or provided by a memory coupled to the processor. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention. Unless stated otherwise, a component such as aprocessor or a memory described as being configured to perform a taskmay be implemented as a general component that is temporarily configuredto perform the task at a given time or a specific component that ismanufactured to perform the task. As used herein, the term ‘processor’refers to one or more devices, circuits, and/or processing coresconfigured to process data, such as computer program instructions.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

A power surge aircraft landing system is disclosed. The system comprisesa processor configured to determine to start a final stage of descentfor the aircraft. The processor also is configured to determine a set ofcommands for actuators of the aircraft, based on the determination tostart the final stage of descent, to flare the aircraft while wings ofthe aircraft are substantially in a forward flight position followed bytransitioning to a vertical tilt position and completing the landing insubstantially vertical flight. For example, the wings may besubstantially parallel to ground in the forward flight position and maybe substantially vertical or tilted away from the aircraft in thevertical tilt position. The processor then provides the set of commands.In some embodiments, the processor automatically determines to start afinal stage of descent for the aircraft in the event the aircraft issubstantially close to ground. The processor may be configured toautomatically determine to start an initial stage of descent for theaircraft and later automatically determine to start a final stage ofdescent.

In some embodiments, the aircraft landing system executes a bird-likelanding process. For example, a bird flies close to the ground beforerapidly flapping its wings and landing. The system may initially causethe aircraft to dive. The aircraft may use minimal amounts of batterypower while in an initial dive. After the aircraft has dove close toground, the system may be triggered to provide instructions for finaldescent. The aircraft may automatically determine to provideinstructions for final descent or may receive a pilot indication. Infinal descent, the system may command the aircraft to sharply pull awayfrom ground. Large amounts of power may be used during final descent.Final descent may take course over a short period of time, such as a fewseconds. The power surge landing system may target a landing site andplan the trajectory of the aircraft to maximize use of the aircraft'swings, minimize energy use, and land with little to no forward speed.The aircraft landing system may enable the aircraft to land in anautomated, power-efficient, safe, planned, and controlled manner. Thesystem may enable the aircraft to land in a predetermined spot withoutrolling or skidding. The aircraft landing system may control rotors andtiltwings of an aircraft during the landing process. Manuallycontrolling the aircraft to land may be imprecise or require greaterbattery power.

FIG. 1 is a diagram illustrating an embodiment of an aircraft's batterydischarge curve. The power surge landing system may be utilized inelectric aircraft. Electric aircraft may be powered by one or morebatteries. The one or more batteries may discharge according to thepattern shown. As shown, when 100% of the battery capacity is available,the battery provides 4.4 Volts. Towards the end of the battery's life,when around 5% of the battery capacity is available, the batteryprovides 3 Volts. Towards the end of a battery's charge, the voltagesupplied may drop off quickly. The battery may have limited or low powercapabilities when it is closed to be being fully drained.

In some embodiments, a battery that powers an electric aircraft is notrecharged while the aircraft is airborne. Towards the end of anaircraft's flight, the aircraft's batteries may be drained to lowlevels. At the low levels, the amount of power that the batteries areable to supply may be limited. Traditional landing systems may require alarge amount of power. In a traditional landing system, the aircraft mayhover and slowly approach ground. Hovering may induce risks ofoverheating the aircraft's systems, overloading the aircraft's motors,or destabilizing the aircraft. For example, an aircraft may be easilydisturbed while hovering by a gust of wind. In some embodiments, theaircraft may be forced to begin descend when the batteries are 50%capacity or more in order to ensure enough battery power is availablefor the landing process.

FIG. 2 is a diagram illustrating an embodiment of power used by anaircraft utilizing a power surge landing system. The graph shows powerused by the aircraft throughout landing. The amount of power used is lowin the beginning of the landing process and spikes near the end of thelanding before dropping to zero. A power surge landing system may directan aircraft to dive until the aircraft is almost at ground. The aircraftmay be in cruise while it dives down. Cruising may cool down aircraftcomponents and safeguard against overheating. The aircraft may retainvelocity in cruise and be relatively resistant to disturbances. A shortdistance above ground, the aircraft may be reared back at full power fora short period of time. Applying a large amount of power in a shortperiod of time may provide less heat to the engine and other criticalaircraft components than applying a lower amount of power over a longperiod of time as in traditional landing.

In a traditional landing, the aircraft may utilize a large amount ofpower through the entire landing. The power surge landing system mayexecute a landing that conserves power overall compared to atraditionally executed landing that involves hover. The power surgelanding system may allow the aircraft to fly further than a traditionallanding system, because a smaller amount of battery power needs to beconserved for landing.

FIG. 3 is a diagram illustrating an embodiment of an aircraft comprisinga power surge landing system. In the example shown, aircraft 300comprises power surge landing system 302. Power surge landing system 302may be stored in aircraft 300. In some embodiments, power surge landingsystem 302 comprises components that are wired up to different parts ofthe airplane, such as the tail, wings, and flaps.

FIG. 4 is a diagram illustrating an embodiment of a power surge landingsystem. The power surge landing system may automate the power surgelanding method in the aircraft. Landing the aircraft in a power surgemethod (e.g. diving and pulling away at maximum power levels close toground) may be difficult, unsafe, or unfeasible to be performedmanually. The system may cause the aircraft to converge at ground at apredetermined rate, begin tilt, slam to full upwards tilt at a specificmoment above ground, and kill throttle as soon as the aircraft touchesground. The system may determine the correct timing of actions andexecute them accurately. Landing the aircraft in a power surge methodmanually may be unpredictable or unsafe.

In the example shown, power surge landing system 400 comprises lidar402, radar 404, camera 406, interface 408, manual controls 410,processor 414, and actuator controllers 412. Lidar 402, radar 404, andcamera 406 may be affixed to the aircraft. In some embodiments, theaircraft comprises one or more sensors. The lidar, radar, camera, andany other appropriate sensor may collect sensor data related to theaircraft. The sensor data may comprise a distance from ground,acceleration or velocity, degree of tilt, or any other appropriateinformation. The sensor data may comprise information regardingobstacles that may prevent the aircraft from landing or diving inspecific areas. Sensor data may be provided by lidar 402, radar 404, andcamera 406 to interface 408.

Interface 408 may also receive instruction from manual controls 410.Manual controls 410 may comprise one or more inceptors that a pilot isable to manipulate. For example, a joystick, a button, a lever, anelectrical mechanism, or a mechanical mechanism may be accessible to thepilot. The pilot may initiate a landing sequence, direct the aircrafttowards a new landing location, or any other appropriate action.

Received data may pass from interface 408 to processor 414. Processor414 may determine a stage of descent for the aircraft based on sensordata and other data received. In some embodiments, the processor isprovided a desired landing location. The processor may determine when toproceed with each stage of descent based on the provided landinglocation. Sensor data, such as wind speed, may be considered. Aircraftlimitations such as maximum throttle levels may be considered. In theevent sensor data reveals an obstacle such as high winds or otherairborne objects in the aircraft's trajectory, the processor maydetermine a new trajectory for the aircraft. The processor may directthe aircraft to fly to a new location and approach the landing locationfrom a different angle.

In some embodiments, the processor may determine to initiate descent.The processor may initiate descent in the event the aircraft batterylevels are low, the aircraft is experiencing a component malfunction, orany other appropriate situation. The processor may initiate descentbased on sensor information.

Processor 414 may provide instructions to actuator controllers 412.Actuator controllers 412 may control actuators of the aircraft.Actuators may comprise a flap, a rotor, or any component of the aircraftthat changes its trajectory. The actuator controllers may be electrical.The processor may be wired to the actuators or actuator controllers.

FIG. 5A is a diagram illustrating an embodiment of an aircraftcomprising a power surge landing system. In some embodiments, the powersurge landing system is utilized in electric aircraft. Electric aircraftmay have reduced power abilities compared to non-electric aircraft.Electric aircraft may require a landing system that utilizes a lowamount of power such as the power surge landing system.

In some embodiments, the power surge landing system is utilized in asmall form factor aircraft. Smaller aircraft may have lower wingloading. Smaller aircraft may be more aerolastic than large aircraft orhave a higher weight to thrust mass ratio. The power surge landingsystem may be utilized in a winged aircraft, rotor-powered aircraft,multi-rotor aircraft, or mixed-mode aircraft.

The power surge landing system may utilize all of an aircraft'savailable actuators in each stage of descent. The system may adapt tovarious configurations of aircraft. The actuators of the aircraft may beconfigured to optimize the position of the aircraft for each stage ofdescent. In some embodiments, the power surge landing system is utilizedin a tiltwing aircraft with multiple rotors. Aircraft 500 as showncomprises wings 502 and 504. Rotors 506 and 508 are affixed to the frontof wing 502. Rotors 510 and 512 are affixed to the front of wing 504.Rotors 506 and 510 are to the left of the fuselage of the aircraft asshown and rotors 508 and 512 are to the right of the fuselage. Wings 502and 504 may be capable of tilting up to 90 degrees, perpendicular to thefuselage. The rotors may face upwards when the wings are fully tilted.The wings and rotors may be utilized by the power surge landing system.

FIG. 5B is a diagram illustrating an embodiment of an aircraftcomprising a power surge landing system. In some embodiments, the powersurge landing system is used in a fixed wing aircraft. In the exampleshown, aircraft 550 comprises wings 552 and 556. The wings may be fixedon the aircraft at a predetermined angle. The wings may be fixed at ashallow angle from the aircraft's fuselage. As shown, wing 552 isattached to a fuselage of the aircraft towards the back of cockpitwindow 554. Wing 556 is attached near the nose of the aircraft, belowcockpit window 554. In the example shown, aircraft 550 comprises wheel558. The aircraft may pivot on one or more wheels. The power surgelanding system may command the aircraft to dive or pull up in order tochange the wings' angles from ground during landing. In someembodiments, the aircraft may land in a tilted position wherein theaircraft's nose is tilted away from the ground. After touching ground,the aircraft's fuselage may pivot on the one or more wheels until it isupright or parallel to ground.

FIG. 6A is a diagram illustrating an embodiment of a tiltwing aircraftin a neutral wing position. In the example shown, aircraft 600 is shownfrom a side view. Rotors 602 and 608 are directed toward the nose of theaircraft. Wings 604 and 608 are in a traditional position. The wings maylie flat atop the aircraft. The aircraft comprises tailpiece 610. Thefuselage of the aircraft is supported by wheels 612 and 614. Theaircraft may be configured to have a neutral wing position whilecruising.

FIG. 6B is a diagram illustrating an embodiment of a tiltwing aircraftin a tilted wing position. In the example shown, the wings of aircraft600 are fully tilted. The wings may be tilted upwards and back. Wings604 and 608 are normal to aircraft 600. Rotors 602 and 606 are parallelto ground.

FIG. 7A is a diagram illustrating an embodiment of a landing processenacted by a power surge landing system in a tiltwing aircraft. Theentire landing run may be shorter than a traditional landing run. Thesystem may automatically direct an aircraft through the positions shown.Positions 700, 710, 720, and 730 show an aircraft in different stages ofdescent.

Position 700 may illustrate an initial stage of descent. In the initialstage of descent, the power surge landing system may instruct theaircraft to dive or to approach at a stabilized speed and descent anglewith low, none, or negative power consumption. In position 700, theaircraft is angled towards ground. The aircraft may utilize minimalamounts of power in the initial stage of descent. In some embodiments,the motors and motor controllers are capable of substantially more powerover very short time periods, possibly up to double of steady-statepower for a few seconds. In the initial stage of descent, descentthrough blown windborne flight may be used to reduce motor load duringthe initial transition from forward flight to hover to reduce the timeand the initial heating of the power system prior to the final use ofpower at extremely low speeds. For example, a vehicle may use half ofhover power to generate lift at a 7 m/s forward flight speed.

The initial stage of descent may be triggered based on a pilotindication. The system may determine when to begin descent based on atarget landing area. The power surge landing system may instruct theaircraft to maintain a dive or initial descent position for the majorityof the landing approach. Prior to descent, wings 702 and 704 may be in aneutral position. In the initial stage of descent, the power surgelanding system may instruct wings 702 and 704 to begin to tilt away froma neutral position. As shown, wings 702 and 704 are tilted slightly awayfrom parallel. In some embodiments, no power is supplied to rotors 706and 708. The combination of wing and rotor lift with some forward speedmay be able to support the vehicle down to a low landing speed. Belowthe low landing speed, gravity may cause the aircraft to fall towardsground. The aircraft may apply a large amount of power to slow theaircraft as it falls, allowing the aircraft to slowly accelerate towardsthe ground in an arc. The trajectory of speed, tilt, control inputs, andaltitude may be optimized to allow the aircraft to touch down accuratelyin a planned position.

Position 710 may illustrate the beginning of a final stage of descent.The aircraft may be flying in at the edge of stall, and at 710, a shortburst of power is applied. In some embodiments, the burst of power isapplied for only a few seconds or long enough for the aircraft to flyabout 10 meters before the aircraft lands. In the final stage ofdescent, the aircraft may pull sharply upwards, away from the ground.The aircraft may pull upwards to better orient the propellers to countergravity. The aircraft may transition into a vertical flight position andcomplete the landing in substantially vertical flight. For example, afixed wing aircraft may be substantially parallel to ground with itswings substantially parallel to ground. A tiltwing aircraft's wings maybe tilted at a vertical angle. The aircraft may pull away from theground at maximum power. The throttles may be ramped up. As shown, thenose of the aircraft is tilted upwards and the aircraft is beginning topull up. In the example shown, wings 712 and 714 further tilt away fromthe nose of the aircraft. Rotors 716 and 718 may be at full power.

Position 720 may illustrate a final stage of descent. The nose of theaircraft as shown is sharply angled away from ground. The aircraft maybe in a full upwards tilt position, e.g. tilted as far as the aircraftcontrols or actuators allow. The trajectory of the aircraft may allow itto slow down before touching down. The surface of the wings may providedrag that aids in slowing the aircraft. Wings 722 and 724 as shown arein a fully tilted position. The wings are perpendicular to the aircraft.Rotors 726 and 728 face upwards and are parallel to the fuselage of theaircraft. The rotors may be powered at maximum power, pulling theaircraft backwards and away from ground.

In some embodiments, the aircraft drops in an arc from position 720 toground in position 730. In a final stage of descent, the aircraft may beincapable of generating enough lift to counteract gravity. The aircraftmay generate an amount of lift that helps slow the descent of theaircraft. Wings of the aircraft may be stalled while also producing alift factor that slows down the aircraft. The wings may produce attachedlift. The aircraft may set down as the attached lift dies out. In thefinal stage of descent, abortion of the final stage of descent may beimpossible. In some embodiments, the aircraft has a thrust to weightratio of 1 or greater before the final stage of descent. The aircraftmay have a thrust to weight ratio of less than 1 but substantially closeto 1 (e.g. 0.9) during the final stage of descent.

The final stage of descent may be very short, for example, a fewseconds. The power surge landing system may enable an aircraft to touchdown with little or no forward speed without hovering. The power surgelanding system may enable an aircraft that is incapable of hover to landat a specific planned location with little or no skidding or rolling.

In some embodiments, the power surge landing system tracks theaircraft's power levels. The system may determine a time or position tobegin initial descent based on a desired landing location. The time orposition may be calculated in order to ensure the aircraft will have asufficient amount of power to carry out the final stage of descent. Inthe event the system detects that the aircraft does not have enoughpower to carry out the final stage of descent, the power surge landingmay be aborted. The system may abort during the initial stage of descent(i.e. cruise descent). Aborting the power surge landing may compriseallowing the aircraft to perform a rolling or skidding landing. Theaircraft may cruise descend until it reaches ground. The aircraft mayland with significant forward speed.

The system may recalculate and change the course of the aircraft'slanding after beginning initial descent. For example, the system mayadjust the aircraft's trajectory based on disturbances. Disturbances maycause the aircraft to veer from its commanded or predicted trajectory.In the event the aircraft is at a higher altitude than it was commandedto be or expected to be during landing, the system may command theaircraft to be tilted back earlier in landing. Less power thanoriginally calculated may be applied. In the event the aircraft isapproaching land at a lower altitude than expected or commanded, thesystem may command the aircraft to tilt less than originally commandedand maximize power. In some embodiments, the system determines arequired power level, degree of tilt of the aircraft, or relatedinstructions for aircraft actuators based on a net loss of lift. The netloss of lift counteracting gravity on the wing may be measured,predicted, or both.

In position 730, the aircraft has landed. The wheels of the aircraft mayhave touched ground. After the aircraft touches ground, throttle levelsmay be turned to zero. Rotors 736 and 738 are parallel to the fuselageof the aircraft. Wings 732 and 734 are fully tilted.

The overall directionality of the aircraft may change rapidly duringdescent. In initial descent, the angle of the aircraft may be 15-30degrees from parallel to ground. The aircraft may be directed towardsground. As final descent begins, the angle may begin to increase in adirection away from ground. In final descent, the aircraft may be angledroughly 45 degrees away from ground. The aircraft may be parallel toground after it touches down. The said angle changes may be associatedin an approach in which wing tilt is not used or is used minimally. Theymay be substantially more level in a case in which significant wing tiltis used.

FIG. 7B is a diagram illustrating an embodiment of wing positioningenacted by a power surge landing system. In position 740, descent hasnot started. The wing edge faces towards the nose of the aircraft. Asdescent begins, the leading wing edge is tilted upwards in position 742.As initial descent begins, the wing is further tilted in position 744.When the power surge is applied to slow down the aircraft, the wings arecompletely tilted in position 746. The wings remain in a fully tiltedupon landing in position 748.

FIG. 8 is a flow diagram illustrating an embodiment of a power surgelanding system process. In some embodiments, FIG. 8 illustrates a basicprocess. In 800, it is determined whether initial descent is triggered.The system may determine whether initial descent is triggered based onsensor data or manual inputs. In the event initial descent is triggered,in 804 initial descent is started. For example, the aircraft may beginto dive towards ground. In 806, it is determined whether final descentis triggered. In the event final descent is not triggered, the processreturns to 804. In the event final descent is triggered, in 808 thesystem starts final descent. The system may apply a power surge and pullthe aircraft sharply away from ground to slow the aircraft inpreparation for landing.

FIG. 9 is a flow diagram illustrating an embodiment of a power surgelanding system process. The process is detailed for a tiltwing aircraft.In 900, it is determined whether descent is triggered. In the eventdescent is not triggered, the process repeats 900. In some embodiments,the process may pause for a predetermined amount of time beforerepeating 900.

In the event descent is triggered, the process proceeds to 902. Descentmay be triggered based on a manual indication or sensor data. In 902, itis determined whether battery levels are low. In the event batterylevels are not low, in 914 hover landing is triggered. The process isfinished. In some embodiments, a traditional landing method using hovermay be used in the event battery levels are not low. A traditionallanding method may be used for pilots that are not familiar with thepower surge process. In the event battery levels are low, a traditionallanding method may be unsafe or unfeasible. In some embodiments, 902 isnot present in a power surge landing system process.

In the event battery levels are low or 902 is not considered, in 904 theaircraft is tilted downwards. In the event the aircraft is a tilt wingaircraft, the wings may be tilted back. In 906, it is determined whetherthe aircraft is in a final stage of descent. Determining whether theaircraft is in a final stage of descent may comprise consolidating andanalyzing environmental information, relative positioning of theaircraft, and a desired landing location. In the event the aircraft isnot in a final stage of descent, the process returns to 904. Theaircraft may remain in its initial descent positioning for the majorityof the duration of the landing. In the event the aircraft is in a finalstage of descent, in 908 the aircraft is pulled back and its wings arefully tilted. In 910, it is determined whether the aircraft has toucheddown. In the event the aircraft has not touched down, the processreturns to 908. In the event the aircraft has touched down, in 912 theaircraft is powered down. For example, throttle may be set to zero. Theprocess is finished.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. An aircraft landing system, comprising: aprocessor configured to: determine to start a final stage of descent forthe aircraft; determine a set of commands for actuators of the aircraft,based on the determination to start the final stage of descent, to flarethe aircraft while at least a plurality of rotors comprising theactuators of the aircraft are substantially in a forward flightposition, followed by transitioning to a vertical flight position of theplurality of rotors and completing the landing in substantially verticalflight; and provide the set of commands to the actuators.
 2. The systemof claim 1, wherein the set of commands are determined based at least inpart on a net loss of lift.
 3. The system of claim 1, wherein theprocessor automatically determines to start a final stage of descent forthe aircraft in the event the aircraft is substantially close to ground.4. The system of claim 1, wherein the processor is configured toautomatically determine to start an initial stage of descent for theaircraft.
 5. The system of claim 4, wherein the initial stage of descentfor the aircraft comprises a low power stage and the final stage ofdescent for the aircraft comprises a high power stage.
 6. The system ofclaim 4, wherein the final stage of descent for the aircraft occurs in ashorter amount of time than the initial stage of descent.
 7. The systemof claim 4, comprising an interface configured to receive sensor data,wherein a determination to start a stage of descent for the aircraft isbased at least in part on the sensor data.
 8. The system of claim 4,wherein a determination to start a stage of descent for the aircraft isdetermined based at least in part on manual controls.
 9. The system ofclaim 7, wherein the sensor data is collected using radar, lidar, or acamera.
 10. The system of claim 4, wherein the initial stage of descentcomprises diving.
 11. The system of claim 4, wherein the aircraft is ina cruise position in the initial stage of descent.
 12. The system ofclaim 1, wherein the aircraft comprises one or more wings that are ableto tilt during flight.
 13. The system of claim 1, wherein the aircraftcomprises two parallel wings that each comprise two rotors positioned onleading edges of the wings.
 14. The system of claim 13, wherein allrotors are at maximum throttle in the final stage of descent.
 15. Thesystem of claim 1, wherein throttle is set to zero in the event theaircraft touches ground.
 16. A method for landing an aircraft,comprising: determining to start a final stage of descent for theaircraft; determining a set of commands for actuators of the aircraft,based on the determination to start the final stage of descent, to flarethe aircraft while at least a plurality of rotors comprising theactuators of the aircraft are substantially in a forward flightposition, followed by transitioning to a vertical flight position of theplurality of rotors and completing the landing in substantially verticalflight; and providing the set of commands to the actuators.
 17. Acomputer program product for landing an aircraft, the computer programproduct being embodied in a non-transitory computer readable storagemedium and comprising computer instructions for: determining to start afinal stage of descent for the aircraft; determining a set of commandsfor actuators of the aircraft, based on the determination to start thefinal stage of descent, to flare the aircraft while at least a pluralityof rotors comprising the actuators of the aircraft are substantially ina forward flight position, followed by transitioning to a verticalflight position of the plurality of rotors and completing the landing insubstantially vertical flight; and providing the set of commands to theactuators.